Cryptolocker ravaged computer users in late 2013 but it was still only the seventh most common form of ransom malware for the second half of the year, Microsoft’s latest Security Intelligence Report (SIR) has calculated using the firm's inhouse Windows user data.

Cryptolocker ravaged computer users in late 2013 but it was still only the seventh most common form of ransom malware for the second half of the year, Microsoft’s latest Security Intelligence Report (SIR) has calculated using the firm's inhouse Windows user data.

Some of this might simply be that Cryptolocker appeared in in September, a relatively late point in the period, but Microsoft’s figure do lay bare the extent of other more traditional types of the ransom attack.

The figures reveal some interesting patterns in the distribution of ransom malware, starting with a confirmation that it is still almost unheard of in some parts of the world such as Latin America, Africa, the Middle East and parts of Asia. This will probably change over time but it is obvious that the targets are largely thriving economies with the money to pay the ransoms demanded.

The most commonly-encountered form was the ‘police warning’ of ‘FBI Trojan’ Reveton, run by a Russian-led single gang reportedly partly broken up by police in February. Encounter rates detected by Microsoft’s own security software varied by country but averaged just above 0.2 percent of Windows users, actually a sharp fall from the rate above 0.4 percent in the third quarter of the year.

Neck and neck with that was Urausy, another police warning Trojan, with an identical encounter rate just over 0.2 percent, leaving a small family or sometimes much more serious forms such as Cryptolocker on very low encounter rates hovering around 0.05 percent.

These rates sound very low but only measure detections made by from the population of users running the firm’s realtime antivirus software (i.e. Windows 8’s Defender) that have opted in to share this data. PCs not running this or where malware was not detected would not count and so these encounter rates surely underestimate Cryptolocker’s prevalence. The crunch figures will be for the first half year figures for 2014, due later this year.

Although some reports have likened the malware in question, Koler.a, to Cryptolocker, this is a huge exaggeration; Koler locks the smartphone screen but can be de-installed whereas Cryptolocker all encrypts data files it finds on a system, which can’t be recovered without the key.